This invention relates to minimization of positioning errors that are experienced by radio locating systems in the presence of multipath signals that arrive from nearby diffractive features and reflective surfaces.
Radiolocation schemes estimate location of objects to be tracked by measuring time parameters that include Time of Arrival or Time Delay of Arrival at a number of receivers at known locations. Other techniques include measuring Angle of Arrival or a composite of time and angle measures.
The accuracy of radiolocating system depends on an accurate time measurement of the time of the incident signal sent by the transmitting device to be located by the network of receiving antennas. In real operating environments it is improbable that only the antenna network receives only an incident (line of sight) signal. The transmitted signal also arrives at the antennas from indirect paths. Reflective surfaces, such as buildings, the ground, surrounding vehicles and other surfaces are sources of undesirable signal paths. Also, the transmitted signal may be diffracted by sharp edges of objects. These phenomena result in the transmitted signals traveling to the antenna networks via non-direct paths. The sum of all signal paths from the transmitter to the receivers results in a composite of multipath signals.
The combined signal at the receivers created by the incident (line of sight) and the diffracted and reflected (non-line of sight) signals creates an uncertainty as to the actual arrival time of the incident signal.
The present invention overcomes the above-described problems in the prior art by providing a method of determining the time of arrival of an incident signal transmitted utilizing a code word that is interspersed with noise and diffracted and reflected signals of the incident signal. The incident, diffracted and reflected signals and noise are collectively defined as a combined signal. The method comprises receiving the combined signal; obtaining the code word to apply to the combined signal; comparing the combined signal with the code word to filter the incident signal and diffracted and reflected signals arising from the incident signal from the combined signal; utilizing the incident signal and related diffracted and reflected signals to determine a first parameter indicative of the incident signal""s time of arrival; and filtering the first parameter utilizing a multipath mitigation algorithm to mitigate the influence of the diffracted and reflected signals to obtain a second parameter indicative of the incident signal""s time of arrival.